ABSTRACT
High-magnitude mechanical strain inhibits bone nodule formation by reducing expression of bone morphogenetic protein-2 (BMP-2), Runt-related transcription factor 2 (Runx2), and muscle segment homeobox 2 (Msx2). Mechanical strain also induces production of proinflammatory factor prostaglandin E2 (PGE2) by osteoblasts. We measured the effect of mechanical strain-induced PGE2 production on bone nodule formation and expression levels of bone formation-related factors. Osteoblast-like cells isolated from fetal rat calvariae were loaded with 18% cyclic tension force (TF) for 48 h in the presence or absence of NS-398, a selective inhibitor of cyclooxygenase-2. To investigate the effect of TF-induced PGE2 on bone formation, bone nodule area on day 21 was measured by von Kossa staining. BMP-2, Runx2, and Msx2 expression levels were examined at 1 day after TF loading. Bone nodule formation was significantly inhibited by TF but was restored to control level by PGE2 inhibition. Furthermore, TF loading-induced reductions in expressions of these factors were restored to control level by PGE2 suppression. These results indicate that PGE2 production induced by high-magnitude mechanical strain inhibits bone nodule formation by reducing expression levels of bone formation-related factors.
Subject(s)
Bone and Bones/pathology , Dinoprostone/biosynthesis , Skull/metabolism , Stem Cells/metabolism , Stress, Mechanical , Animals , Bone Morphogenetic Protein 2/metabolism , Bone and Bones/metabolism , Core Binding Factor Alpha 1 Subunit/metabolism , Cyclooxygenase 2 Inhibitors/pharmacology , Homeodomain Proteins/metabolism , Nitrobenzenes/pharmacology , Rats , Skull/cytology , Sulfonamides/pharmacologyABSTRACT
PURPOSE: Orthodontic tooth movement occurs during the bone remodeling induced by therapeutic mechanical strain. It is important to investigate the relation between the strength of mechanical stress and bone formation activity. The aim of this study was to determine the effect of high-magnitude mechanical strain on bone formation in detail. MATERIALS AND METHODS: Osteoblast-like cells isolated from fetal rat calvariae were loaded with 18% cyclic tension force (TF) for 48 h. To phenotypically investigate the effect of TF, we measured the number and the size of bone nodules stained by von Kossa technique on day 21 after cell seeding and determined the calcium content of bone nodules on day 14. Furthermore, we examined the gene expression of BMP-2, Runx2 and Msx2, which are important factors for bone nodule formation, on days 1, 4 and 7 after TF loading. RESULTS: The maximum bone nodule size in the control group was 1620 and 719 µm in the TF group. Furthermore, the mean number of bone nodules sized over 360 µm in the TF group was significantly decreased compared to the control group. The calcium content was also significantly decreased to 42% by TF loading. The mRNA expression of BMP-2, Runx2 and Msx2 was decreased 1 and 4 days after TF loading. CONCLUSION: The differentiation of bone forming progenitor cells into bone nodule forming cells was inhibited by TF due to the decreased expression of bone formation related factors such as BMP-2, Runx2 and Msx2.
